107 
K7 


UC-NRLF 


THE 


USE  AND  CARE  or  A  BALANCE 


PETER  J,  KRAYER 


JNIVERSITY  FARM 


K7 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 


THIS  BOOK  IS  DUE  ON  THE  LAST  DATE 
STAMPED  BELOW 


5w-10,'22 


THE  USE  AND  CARE  OF  A  BALANCE 


!1818B3BiSHBBIH?fBlBiKH^ijHpffiff|?Bfflj^>3SSP^ 

Published  by 

The  Chemical  Publishing  Company 

EASTON,  PA. 

Publishers  of  Scientific  Boob 

Engineering  Chemistry  Portland  Cement 

Agricultural  Chemistry  Qualitative  Analysis 

Household   Chemistry  Chemists'  Pocket  Manual 

Metallurgy,  Etc. 


THE 

Use  and  Care  of  a  Balance 

BY 

PETER  J.  KRAYER 

NEW  PROVIDENCE.  NEW  JERSEY 


EASTON.  PA. 

THE  CHEMICAL  PUBLISHING  COMPANY 
1913 


LONDON,  ENQLANO:  TOKYO,   JAPAN: 

WILLIAMS  A  NORQATE  MARUZEN  COMPANY,  LTD., 

14  HENRIETTA  STREET,    COVEWT   GARDEN,    W.  C.  11-19  NIHONBA8MI   TORI-SANCHOME 


COPYRIGHT.  1913,  BY  EDWARD  HART 


CONTENTS. 


A  Method  of  Weighing  5 

Setting  Up  a  Balance  5 

Temperature   7 

Testing  a  Balance  for  Zero  Point  9 

Arm  Length 9 

Testing  a  Balance  for  Arm  Length  10 

Testing  for  Sensibility  n 

The  Rider 16 

Improperly  Adjusted  Balances — How  to  Adjust  Them  18 

To  Use  a  Balance  when  the  Arm  Length  is  Incorrect 26 

Rules  to  be  Observed  when  Cleaning  Balances  27 

The  Effect  of  an  Electric  Lamp  28 

Vibration  30 

The  Staudinger  Balance 31 

Assay  Balances  34 

To  Replace  the  Glass  Base  35 

WEIGHTS. 

Kinds  of  Weights  38 

Care  of  Weights 39 

Standard  for  Calibrating  Weights  39 

Calibrating  Weights   40 

Recipe  for  Lacquer  for  Aluminum,  German  Silver  and  Brass . .  42 


The  Use  and  Care  of  a  Balance. 


A  METHOD  OP  WEIGHING. 

For  accurate  weighting  it  is  customary  to  make  a 
Balance  oscillate  four  or  five  divisions  on  each 
side  of  the  zero  point.  To  do  this  the  weigher  is  obliged 
to  force  an  oscillation,  by  means  of  pushing  in  the  pan 
arrest  two  or  three  times,  or  as  often  as  necessary  to 
create  the  necessary  oscillation.  As  the  rider  is  usually 
in  use  on  the  Beam  it  cannot  be  used  for  that  purpose. 
With  a  container,  such  as  a  crucible  or  bulb  that  is  first 
weighed,  then  charged  and  then  weighed  again,  it  is  best 
on  the  first  weighing  to  add,  say  one  milligram  by  moving 
the  rider,  or  make  the  balance  swing  out  to  the  left  five 
divisions  and  back  to  the  zero  point.  On  the  second 
weighing  do  the  same  thing  making  it  swing  out  to  five 
divisions  and  back  to  the  zero  point.  The  weighing  will 
be  correct  as  the  extra  weight  will  be  added  to  the  crucible 
or  bulb  and  not  to  the  object  weighed. 

SETTING  UP  A  BALANCE. 

When  a  balance  has  been  unpacked  and  is  ready  for 
setting  up,  clean  the  balance  case,  pillar,  beam  and 
stirrups.  Screw  the  index  tightly  upon  the  beam,  using 
a  pin  on  indexes  having  a  hole  drilled  in  the  upper  part  for 


6          THE  USE  AND  CARE  OF  A  BALANCE 

that  purpose,  until  the  screw  on  the  little  adjusting 
weight  upon  the  index  is  directly  in  front.  Then  place 
the  beam  into  its  position  by  placing  the  socket  on  the 
beam  onto  the  ball  on  the  beam  support,  at  the  same  time 
lowering  the  beam  supports  about  half  way.  Then 
swing  the  beam  on  the  socket  until  the  bearing  on  the 
other  side  comes  directly  over  the  point.  Raise  the  beam 
support  and  bring  the  beam  into  its  proper  position. 

The  stirrups  are  marked  with  one  dot  (')  or  two  dots 
("),  as  are  the  beam  supports.  They  should  be  placed 
upon  their  supports  according  to  these  marks.  Care 
should  be  taken  that  all  marks  come  to  the  front.  The 
bow  wires  or  pans  are  marked  (')  or  ("),  or  the  pans  are 
stamped  "L"  or  "R"  for  left  and  right  respectively.  In 
placing  the  pans  upon  the  hooks  of  the  stirrups  care 
should  be  taken  at  all  times  to  have  the  marks  to  the 
front,  or  the  letters  so  that  they  can  be  read  correctly 
from  the  front. 

This  point  may  seem  insignificant,  but  as  a  matter  of 
fact  it  is  very  important.  When  bows  are  placed  upon 
the  balance  with  the  marks  to  the  rear  or  the  letters  in  a 
position  to  be  read  backwards  they  are  not  the  same 
position  in  which  they  were  when  the  balance  was  finally 
adjusted  by  the  manufacturer.  This  reversal  of  the  bows 
from  their  correct  positions,  often  throws  them  out  of 


THE  USE  AND  CARE  OF  A  BALANCE  7 

adjustment  with  the  pan  arrests,  causing  the  index  to  go 
to  one  side  of  the  zero  point. 

It  must  be  assumed  that  the  balance  has  been  per- 
fectly adjusted  before  leaving  the  factory  and  that  every 
part  has  been  placed  in  its  proper  position.  The  index 
should  be  firmly  screwed  upon  the  beam,  and  the  screw 
head  of  the  sliding  weight  on  the  index  should  be  facing 
the  front.  If  the  balance  has  been  correctly  adjusted  by 
the  manufacturer,  the  sliding  weight  will  naturally  go 
into  its  proper  position  upon  the  index  being  screwed 
tightly  into  the  beam.  If,  however,  when  the  index  is 
screwed  tightly  into  the  beam,  the  sliding  weight  does  not 
face  properly,  the  weight  should  be  turned  so  as  to  bring 
the  screw  head  to  the  front.  Be  careful  not  to  raise  or 
lower  the  weight  while  doing  so. 

TEMPERATURE. 

The  place  for  setting  up  a  balance  must  be  carefully 
selected  and  pains  must  be  taken  to  insure  uniform  tem- 
perature throughout.  Do  not  allow  the  heat  from  a 
radiator  to  strike  the  beam  from  one  side.  The  heat 
from  any  artificial  heater,  or  even  the  sun,  when  reflected 
more  upon  one  end  of  the  beam  than  on  the  other  will 
cause  a  greater  expansion  of  the  nearer  end  of  the  beam, 
thus  throwing  the  balance  out  of  equilibrium,  by  chang- 
ing the  arm  length. 


8  THE  USE  AND  CARE  OF  A  BALANCE 

The  importance  of  temperature  may  be  illustrated  by 
the  following  experiment : 

Take  two  brass  weights  of  about  10  grams  each. 
Place  the  weights  in  the  balance,  allowing  them  to  remain 
there  for  about  one  half  hour,  in  order  that  they  may 
acquire  throughout  the  same  temperature  as  that  of  the 
interior  of  the  balance.  Place  one  on  each  scale  pan  and 
balance  them  with  the  rider.  Then  with  a  pair  of  forceps 
take  one  weight  out  of  the  balance,  placing  it  in  the  palm 
of  the  hand  and  closing  the  fingers  over  it.  Hold  it  in  this 
manner  for  about  a  minute.  Then  replace  it  upon  the 
scale  pan.  Note  that  they  do  not  now  balance.  To  com- 
plete the  experiment  and  to  fully  appreciate  the  absolute 
necessity  for  uniform  temperature  for  exact  weighing, 
leave  the  rider  in  its  position  on  the  beam.  Allow  the 
weight  thrown  off  by  the  change  in  temperature  to  remain 
on  the  balance  pan,  and  from  time  to  time  test  it,  and 
note  the  length  of  time  required  for  it  to  again  regain 
the  temperature,  as  nearly  as  possible,  of  the  original 
weighing.  When  the  weights  balance,  or  almost  balance, 
it  shows  that  the  weight  experimented  with  has  almost 
regained  the  temperature  of  the  first  weighing. 

There  are  very  few  balances  that  will  not  change  arm 
length  with  a  change  in  temperature.  The  arm  length 
of  a  balance  can  often  be  regulated  with  the  temperature 


THE  USE  AND  CARE  OF  A  BALANCE  9 

in  the  room;  that  is,  the  arm  length  of  a  balance  adjusted 
to  a  temperature  of  85  degrees  may  not  be  equal  in  a 
temperature  of  75  degrees,  but  by  raising  the  temperature 
to  85  degrees  it  will  be  found  to  be  correct. 

TESTING  A  BALANCE  FOR   ZERO   POINT. 

After  a  balance  has  been  set  up  according  to  directions, 
and  time  has  been  allowed  for  temperature,  the  balance 
should  be  carefully  released.  A  perfectly  adjusted 
balance  will  not  oscillate;  but,  all  conditions  being  per- 
fect, the  index  will  remain  stationary  at  the  zero  point. 

To  obtain  an  oscillation  of  the  index,  place  the  rider 
upon  the  beam  at  the  two  milligram  division,  picking  up 
the  rider  as  soon  as  the  beam  is  brought  into  motion.  This 
will  create  the  desired  swing  or  oscillation.  Five  divisions 
on  the  index  plate  are  generally  obtained.  Take  five 
oscillations  in  the  usual  way  to  obtain  the  equilibrium, 
or  zero  point. 

ARM  LENGTH. 

The  distance  on  the  beam,  between  the  bearing  point  of 
the  center  knife-edge  and  the  bearing  point  of  the  right 
end  knife-edge  is  the  right  arm  length.  The  distance  be- 
tween the  bearing  point  of  the  center  knife-edge  and  the 
bearing  point  of  the  left  end  knife-edge  is  the  left  arm 
length. 


IO  THE  USE  AND  CARE  OF  A  BALANCE 

TESTING  A  BALANCE  FOR  ARM  LENGTH. 

First :  Place  the  rider  upon  the  one  milligram  division, 
and  see  how  many  divisions  it  will  indicate  on  the  index 
plate.  It  should  swing  to  five  and  back  again  to  zero. 

Then  place  fifty  grins,  upon  each  pan.  If  the  weights 
are  of  equal  value,  the  zero  point  will  be  retained  as  at 
first,  provided,  however,  that  the  arm  length  of  the  beam 
and  the  line  of  the  knife  edges  are  perfect.  Then  again 
place  the  rider  upon  the  one  milligram  division,  with  the 
50  grams  still  upon  the  pan.  The  index  should  show  five 
divisions  on  the  index  plate  to  be  perfect. 

When  a  balance,  upon  testing  with  fifty  grms.  in  each 
pan,  swings  for  instance,  five  divisions  to  the  right,  and 
by  changing  the  weights  (that  is,  the  weight  from  the 
right  hand  pan  to  the  left  hand  pan,  and  that  from  the 
left  hand  pan  to  the  right,)  the  balance  still  shows  five 
divisions  to  the  right,  the  weights  are  of  equal  value, 
but  the  arm  length  of  the  balance  is  out  five  divisions,  the 
left  arm  being  longer  than  the  right,  so  that  if  the 
sensibility  of  the  balance  was  found  to  be  five  divisions 
to  one  milligram,  the  balance  is  out  one  milligram  on  each 
weighing. 

When  a  balance,  upon  testing  with  50  grams  in  each 
pan,  swings,  say  five  divisions  to  the  right  and  back  to 
the  zero  point,  and  by  changing  the  weights  from  left  to 


THE  USE  AND  CARE  OF  A  BALANCE  II 

right  and  from  right  to  left,  it  swings  five  divisions  to 
the  left,  the  weights  are  out  and  the  arm  lengths  of  the 
balance  are  equal. 

But  if  it  swings  five  divisions  to  the  right  and  three 
divisions  to  the  left,  both  balance  and  weights 
are  inaccurate.  That  is,  the  weights  are  off  three 
divisions  plus  one-half  the  difference  between  five 
divisions  and  three  divisions,  or  two  divisions,  which  is 
one  division.  Three  plus  one  equals  (3  -f-  I  =  4)  four 
divisions  for  the  weight,  and  one  division  for  the  arm 
length  of  the  beam. 

TESTING  FOR  SENSIBILITY. 

When  a  balance,  on  testing  for  sensibility,  shows  five 
divisions  for  one  milligram  without  weight,  and  reduces  in 
sensibility  with  50  grams  in  feach  pan  it  is  due  to  either  of 
two  causes.  First,  the  beam  is  not  constructed  strongly 
enough  to  bear  the  weight;  or,  second,  the  center  knife- 
edge  is  above  the  end  ones,  thus,  as  in  Fig.  i,  caused 
by  the  knife-edges  being  worn,  or  improperly  adjusted. 
If  the  sensibility  should  increase,  then  the  knife-edges 
are  as  in  Fig.  2,  that  is,  the  center  knife-edge  is  lower 
than  the  end  ones.  In  either  case  the  sensibility  cannot 
be  made  uniform  by  the  adjusting  weight  upon  the  index. 

If  the  sensibility,  with  and  without  weights,  remains 


12 


THE  USE  AND  CARE  OF  A  BALANCE 


the  same,  then  the  knife-edges  are  as  in  Fig.  3,  that  is, 
they  are  in  a  perfect  line. 

If  the  knife-edges  are  found  to  be  as  in  Figs.  I  and  2, 
the  sensibility  cannot  be  regulated  by  the  weight  for  that 
purpose  on  the  index.  In  Fig.  I,  the  more  weight  placed 


rl 


Fig.    i. 


Fig.   2. 


Fig.   3. — Beam. 

upon  the  pans,  the  less  sensitive  it  becomes ;  in  Fig.  2,  with 
each  addition  of  weight  in  the  pans,  the  sensibility 
increases  up  to  the  point  where  the  beam  begins  to  bend ; 
it  will  then  gradually  decrease,  and  continue  to  decrease 
as  weight  is  added. 

In  Fig.  3,  however,  the  sensitiveness  can  be  regulated  at 


THE  USE  AND  CARE  OF  A  BALANCE  13 

any  desired  sensitiveness,  five  or  ten  divisions  upon  the 
index  plate  for  one  milligram,  and  will  remain  so  up  to 
the  point  where  the  beam  begins  to  bend.  When  this  point 
is  reached  care  should  be  taken  not  to  exceed  this  weight, 
for  it  will  injure  the  balance  if  too  frequently  done. 

If  a  balance,  when  tested,  is  found  as  in  Fig  3,  the 
latter,  after  being  in  use  for  some  time,  it  is  found  as  in 
Fig.  i,  the  knife-edges  have  become  worn,  and  must  be 
sharpened  and  brought  back  to  their  former  position. 


Fig.   4. 

4>  5  and  6  show  three  views  of  the  Sartorius 
beam.  Fig.  4,  shows  the  front  view  of  the  end  of  the 
beam,  without  the  knife-edge.  Fig.  5  shows  end  view  of 
beam  with  knife-edge  upon  it.  Fig.  6,  shows  front  view 
of  end  of  beam  with  knife-edge  upon  it. 

By  viewing  Fig.  4,  it  will  be  seen  that  the  ends  thereof 
are  slit,  thus  having  two  parts.  It  will  be  seen  further 

2 


14  THE  USE  AND  CARE  OF  A  BALANCE 

that  a  hole  is  drilled  through  the  lower  part.  This  hole 
is  partly  threaded  and  a  steel  pin  is  inserted  into  it;  a 
screw  is  then  screwed  in  forcing  the  pin  up  against  the 


Fig.   5. 

under  side  of  the  top  of  the  beam.  Often  when  removing 
this  screw,  the  pin  drops  out  and  is  lost,  causing  much 
annoyance. 

In  Fig.  6,  two  screws  will  be  observed,  marked  "A"; 


Fig.  6. 

three  screws  marked  "D";  one  screw  marked  "C"  and 
one  marked  "E." 


THE  USE  AND  CARE  OF  A  BALANCE  15 

If,  when  testing  a  balance,  the  knife-edges  are  found 
as  in  Fig.  i  loosen  two  screws  (Fig.  6)  marked  "A,"  and 
three  screws  "D"  and  fasten  screw  "C"  so  as  to  force  the 
steel  pin  up  against  the  under  side  of  the  top  of  the  beam, 
thus  forcing  the  latter  up  in  turn.  Then  fasten  two 
screws  "A"  until  the  knife-edges  are  found  as  in  Fig.  3. 

The  arm  length  is  adjusted  by  the  screw  "E"  upon  the 
side  found  to  be  the  shortest,  by  unscrewing  the  screw 
"E"  until  the  arm  length  is  found  to  be  equal. 

Some  Sartorius  balances  have  a  sliding  weight  upon 
the  index,  others  have  a  sliding  weight  upon  the  beam  and 
still  another  kind  has  a  screw  extending  up  and  down  be- 
tween two  upright  parts  of  the  beam  in  the  center,  for  the 
purpose  of  adjusting  the  sensibilities. 

The  following  rules  for  adjusting  for  sensibility  in 
these  balance  are  applicable  only  in  the  last  two  cases : 
To  raise  the  sensibility,  raise  the  sliding  weight  or  screw 
(in  the  last  mentioned  case,  screw)  on  the  beam  for  that 
purpose,  upward.  To  lower  the  sensibility,  lower  the 
sliding  weight,  or  screw  downward  the  screw  on  the 
beam  for  that  purpose. 

On  balances  having  the  sliding  weight  on  the  index 
the  adjustment  for  sensibility  is  made  in  the  same  manner 
as  on  other  balances ;  that  is,  to  raise  the  sensibility,  raise 
the  weight  and  to  lower  it,  lower  the  weight. 


i6 


THE  USE  AND  CARE  OF  A  BALANCE 


THE  RIDER. 

The  graduation  on  the  beam  has  for  its  object  the 
doing  away  with  small  weights  below  five  or  ten  milli- 
grams. Therefore,  to  determine  the  weight  of  the  rider 
required  on  the  balance  it  is  well  to  know  that  the  dis- 
tance between  the  center  knife-edge  and  the  end  knife- 


edge  is  divided  into  a  given  number  of  parts,  usually  five 
or  six,  and  ten  or  twelve ;  each  of  these  subdivided  into 
five  or  ten  parts. 

Some  beams  have  an  extension  over  the  end  knife-edge, 
as  in  Fig.  7,  while  others  have  not,  as  in  Fig.  8.    In  the 


Fig.  8. 


case  of  Fig.  7,  the  rider  may  be  placed  directly  over  the 
knife-edge  and  the  beam  may  be  divided  into  five  or  ten 
parts,  the  rider  weighing  five  or  ten  milligram,  corres- 
ponding with  a  five  or  ten  milligram  weight  in  the  opposite 
pan.  Thus  each  part  corresponds  to  one  milligram. 


THE  USE  AND  CARE  OF  A  BALANCE  17 

In  the  case  of  Fig.  8,  however,  the  beam  must  be 
divided  into  six  or  twelve  parts,  so  that  the  rider  weigh- 
ing six  or  twelve  milligrams  when  placed  upon  the  five  or 


Fig.    9. — Pillar. 

ten  division  will  correspond  with  a  five  or  ten  milligram 
weight  in  the  opposite  pan ;  so  that,  while  the  number  five 
or  ten  may  be  the  largest  stamped  on  the  beam,  that  does 
not  signify  the  weight  of  the  rider  required. 

The  rider  is  carried  along  on  the  beam  by  a  hook  upon 


l8  THE  USE  AND  CARE  OF  A  BALANCE 

a  rod  called  the  rider-rod.     This  rider-rod  should  run 
parallel  with  the  beam. 

Very  often  the  thumb  screws  that  fasten  the  stand  or 
pillar  to  the  case  become  loosened  and  allow  the  pillar 
to  turn,  so  that  the  beam  is  no  longer  parallel  with  the 
rider-rod.  This  may  occur  in  shipment  or  later,  the 
shrinking  of  the  wood  in  the  case;  or  the  washers  (some 
having  washers  between  the  metal  nuts  and  the  glass 
plates),  causing  the  riders  to  be  thrown  from  the  beam. 
To  correct  this  error  turn  the  pillar  so  that  the  beam  is 
again  brought  parallel  with  the  rider-rod  and  fasten 
the  pillar  to  the  case  by  the  two  thumb  screws  marked 
"A"  in  Fig.  9. 

IMPROPERLY  ADJUSTED  BALANCES, 
HOW  TO  ADJUST  THEM. 

Note  i. — When  a  beam  is  supported  the  center  knife- 
edge  should  be  free,  so  that  day  light  can  be  seen  between 
the  knife-edge  and  the  plane.  The  same  should  be 
observed  in  the  end  knife-edges,  between  the  knife-edges 
and  the  stirrup  planes.  When  the  center  knife-edge  rests 
upon  the  center  plane,  that  is  the  beam  supports,  Fig.  10, 
do  not  raise  the  beam  sufficiently  to  see  daylight  between 
the  center  knife-edge  and  the  plane,  while  daylight  can 
be  seen  between  the  end  knife-edges  and  the  stirrup 
planes,  (the  thumb  screws  "A,"  Fig.  9,  being  firmly 
fastened)  ;  then  the  beam  must  be  raised  by  means  of 


THE  USE  AND  CARE  OF  A  BALANCE  19 

the  screws  "A,"  "A"  in  the  Beam  Support,  Fig.  10,  until 


daylight  can  be  seen  between  the  center  knife-edge  and 
the  plane. 


2O         THE  USE  AND  CARE  OF  A  BALANCE 

In  so  doing  always  observe  the  index,  keeping  the 
point  at  the  zero  point  on  the  index  plate.  Sometimes 
the  screws  "A,"  Fig.  10  become  loosened  and  by  so  doing 
lower  the  beam  supports,  and  the  beam  can  be  raised 
to  its  proper  position  by  fastening  them. 

Note  2. — When,  on  releasing  the  beam  the  index 
deviates  to  the  right  or  left,  and  back  to  the  zero  point, 
before  releasing  the  pan  rests,  it  is  an  indication  that  one 
stirrup  is  raised  more  from  the  knife-edge  than  the  other, 
If  the  index  deviates  to  the  left,  then  the  left  hand  stirrup 
is  raised  more  from  the  knife-edge  than  the  right.  If 
the  stirrup  support  is  raised  from  Fig.  10,  the  left  hand 
stirrup  should  be  lowered  by  means  of  the  screws  "E," 
"E"  (Fig.  10)  until  the  index  does  not  deviate  but  re- 
mains perfectly  stationary  at  the  zero  point.  If  it  is  found 
that  the  stirrup  support  rests  firmly  upon  Fig.  10  on  the 
left  hand  side,  then  the  right  hand  stirrup  must  be  raised 
by  means  of  the  screws  "E,"  "E"  on  the  right  hand  side, 
until  the  index  does  not  deviate,  but  remains  perfectly 
stationary  at  the  zero  point. 

Note  j. — When  the  index  deviates  to  the  right  and 
back  again  to  the  zero  point,  then  the  right  hand  stirrup 
is  raised  more  from  the  knife-edge  than  the  left.  If 
the  stirrup  support  is  raised  from  Fig.  10  on  the  right 
hand  side,  the  right  stirrup  should  be  lowered  by  means 


THE  USE  AND  CARE  OF  A  BALANCE  21 

of  the  screws  "E,"  "E"  (Fig.  10)  on  the  right  hand  side, 
until  the  index  does  not  deviate  from  the  zero  point  (or 
the  stirrup  support  rests  upon  Fig.  7).  If,  when  the 
stirrup  support  rests  upon  Fig.  10,  the  index  still  deviates 
to  the  right,  it  is  adjusted  by  raising  the  stirrup  support 
by  means  of  the  screws  "E,"  "E"  Fig.  10,  on  the  left 
hand  side,  until  the  index  does  not  deviate  but  remains 
perfectly  stationary  at  the  zero  point. 

Note  4. — When  the  beam  is  arrested  and  the  index  does 
not  point  to  the  zero  point  on  the  index  plate,  the  index 
not  having  been  bent  by  accident,  it  is  caused  by  the 
loosening  of  screw  "D,"  Fig.  10.  In  this  case,  if  the 
index  points  to  the  left  it  will  be  found  that  the  right 
hand  stirrup  is  raised  more  from  the  knife-edge  than  the 
left,  and  the  center  knife-edge  rests  upon  the  plane, 
screw  "D"  on  the  right  hand  side  of  Fig.  10  should  be 
raised  until  daylight  can  be  seen  between  the  knife-edge 
and  the  plane,  when  the  index  points  to  the  zero  point. 
If,  when  the  index  is  brought  to  the  zero  point,  and  the 
stirrups  are  in  proper  position,  and  the  center  is  still  not 
brought  into  its  proper  position,  further  adjustment  must 
be  made  by  the  screws  "A,"  "A,"  Fig.  10,  until  daylight 
can  be  seen  between  the  center  knife-edge  and  the  plane. 

Note  5. — When  the  index,  upon  arresting  the  beam, 
deviates  back  towards  the  index  plate,  it  will  be  found 


22 


THE  USE  AND  CARE  OF  A  BALANCE 


that  the  end  knife-edges  and  the  stirrup  planes  are  not 
parallel.  On  balances  not  having  adjustment  upon  the 
beams,  as  in  Fig.  n,  it  will  be  seen  that  the  planes,  upon 
either  the  right  or  left  hand  stirrup  or  both  strike  the 
knife-edge  upon  one  point  and  slide  into  position.  They 
should  be  adjusted  by  the  screws  "E"  Fig.  10.  When  the 
index  goes  back  to  the  index  plate,  the  stirrup  support 


Fig.    ii. 

should  be  raised  by  the  front  screw  "E,"  Fig.  10,  until  the 
knife-edge  and  plane  are  parallel.  When  the  index  de- 
viates towards  the  front,  away  from  the  index  plate,  then 
the  stirrups  are  in  opposite  positions  and  adjustment  is 
made  by  the  back  screw  "E,"  Fig.  10  until  knife-edges 
and  plane  are  parallel.  In  balances  having  upon  the 
beam  for  a  support  an  adjustment  such  as  Fig.  n,  the 
index  deviating  back  towards  the  index  plate,  it  is  ad- 


THE  USE  AND  CARE  OF  A  BALANCE 


justed  by  screwing  down  screw  I,  Fig.  n,  and  if  the 
index  deviated  out  from  the  index  plate  it  is  adjusted  by 
screwing  down  screw  2,  Fig.  n,  until  index  does  not 
deviate.  (This  adjustment  is  not  favored  by  the  writer 


Fig.  12. — Stirrup. 


Fig.    i2&.} — Stirrup   and   support. 

for  the  reason  that  it  conceals  an  error  that  may  exist 
as  in  Note  5).  The  distance  between  the  center  knife 
edge  and  the  plane  where  the  beam  is  supported  and  the 
distance  between  the  end  knife  edges  should  be  equal. 


THE  USE  AND  CARE  OF  A  BALANCE 


Note  6. — The  stirrups,  Fig.  12,  should  balance  per- 


Fig.  i2b. — Sartorius  stirrup. 


Fig.    i2c. 

fectly  upon  the  knife-edges;  that  is,  first  remove  the  bow 
from  the  right  hand  side,  then  gently  release  the  beam ;  if 


THE  USE  AND  CARE  OF  A  BALANCE 


the  lower  part  of  the  stirrup  or  hook  swings  in  towards 
the  pillow,  and  by  tapping  the  base  gently  with  the  hand, 
the  stirrup  falls  off  the  knife-edge,  the  stirrup  support, 
which  supports  the  stirrup,  extends  out  too  far.  By 
loosening  screw  "B,"  Fig.  10,  one  screw  "C"  in  front  the 
stirrup  support,  Fig.  10  can,  by  a  gentle  pressure  in  to- 
wards the  pillar,  be  brought  to  its  proper  position  so  that 
it  will  balance  the  stirrup  upon  the  knife  edge.  If  the 
stirrup  swings  out  from  the  pillar,  then  the  stirrup  sup- 


|o  ofr 


C 

Fig.   13. — Pan  arrests. 

port  must  be  brought  out  until  the  stirrup  balances  on  the 
knife-edge,  then  fasten  screws  "B"  and  "C."  Upon  the 
Sartorius  Balance  the  pillar  "C"  must  be  shifted  in  the 
place  of  stirrup  support  on  the  Becker  and  Troemner 
Balances.  Upon  releasing  a  balance,  the  pan  should 
lightly  touch  the  pan-arrest.  If,  upon  releasing  the 
beam,  the  index  does  not  remain  at  the  zero  point,  it  is 
adjusted  by  the  milled  head  screw  upon  the  right  hand 
side  of  the  pan  arrest,  or  scale-stop.  The  Becker  has  only 
one  of  these  crews,  while  the  Troemner  has  one  on  each 
side. 


26 


THE  USE  AND  CARE  OF  A  BALANCE 


TO  USE  A  BALANCE  WHEN  THE  ARM  LENGTH 

IS  INCORRECT. 

A  balance  of  unequal  arm  length  may  be  used  by  adding 
or  subtracting  the  amount  of  the  error,  or  by  changing 
the  theoretical  zero  point  on  the  index  plate.  For 


Fig.    14. — Bow   and   pan. 


instance:  If  the  arm  length  is  five  divisions  out  either 
way  to  the  left  or  right  with  fifty  grms.,  the  index  swings 
out  five  divisions  and  back  again  to  the  zero  point,  the 


THE  USE  AND  CARE  OF  A  BALANCE 


zero  point  would  be  two  and  one-half  divisions  in  the 
direction  in  which  it  swings,  and  in  weighing,  that  would 
constitute  the  theoretical  zero  point. 
RULES  TO  BE   OBSERVED  WHEN  CLEANING   BALANCES. 

First. — Remove  the  bows  and  stirrups. 

Second. — Take  hold  of  the  index,  or  pointer,  with  the 


Fig.  15. — T  for  beam  support. 

right  hand,  with  a  gentle  pressure  to  the  right,  and  turn- 
ing the  key  with  the  left  hand,  bring  the  right  end  of  the 
beam  forward  and  the  beam  will  follow  it.  Take  a  clean 


28 


THE  USE  AND  CARE  OF  A  BALANCE 


cloth  and  wipe  the  knife-edges  and  center  and  end  bear- 
ings. Then  with  a  camels  hair  brush  carefully  remove  all 
dust  from  the  beam  stirrups  and  other  parts,  particularly 
from  the  planes,  as  they  should  always  be  as  free  as 
possible  from  dust.  To  replace  the  beam,  lower  the 
beam  supports  by  using  the  key,  and  place  the  socket 
on  the  ball ;  then  bring  the  other  end  of  the  beam  around 
until  the  center  knife-edge  is  over  the  center  bearing. 
At  the  same  time  raise  the  beam  supports.  Replace  the 
stirrups  and  hangers  after  cleaning  and  dusting. 


Fig.    1 6.— Key. 

Third. — Let  the  balance  stand  for  about  one-half  hour, 
in  order  to  allow  the  temperature  to  become  uniform. 

Fourth. — The  friction  caused  while  wiping  glass 
apparatus,  such  as  glass  pans,  watch  glasses,  etc.,  with  a 
cloth  for  cleaning  purposes,  electrifies  the  glass.  The 
charge  may  be  quickly  dissipated  by  gently  breathing 
upon  the  glass.  As  a  matter  of  fact  this  acts  instantane- 
ously. The  glass  should  then  be  placed  in  the  balance 
and  a  little  time  should  be  allowed  for  temperature. 


THE  USE  AND  CARE  OF  A  BALANCE  29 

THE  EFFECT  OF  AN  ELECTRIC  LAMP. 

Fifth. — Do  not  place  electric  lights  too  close  to  the  top 
of  the  balance  case,  in  order  to  maintain  the  uniformity 
of  temperature. 

When  an  electric  lamp  is  placed  over  the  top  of  a 
balance,  so  that  the  heat  from  the  lamp  affects  the  balance 
—the  more  powerful  rays  of  heat  strike  the  center  of  the 
beam,  and  naturally  the  temperature  of  that  part  of  the 
beam  is  higher  than  the  ends,  and  causes  the  beam  to  ex- 
pand from  that  point,  with  the  result  that,  although  it 
may  not  affect  the  arm  length,  it  will  lower  the  end  knife- 
edges  and  reduce  the  sensibility  of  the  balance.  It  will 
be  readily  seen  that  repeated  changing,  in  turning  on  and 
off  the  light  will  in  time  have  its  ill  effects  on  the  balance, 
by  permanently  reducing  the  sensibility  and  also  effect- 
ing the  arm  length.  It  is  best  to  have  artificial  light  come 
from  in  front  of  the  balance. 

Sixth. — Use  a  little  kerosene  oil  on  a  cloth  with  which 
to  clean  the  case,  for  it  brightens  the  polish  without 
injuring  it. 

Seventh. — Do  not  use  sulphuric  acid  for  a  drier  in  a 
balance  having  steel  knife-edges.  If  a  drier  is  used, 
calcium  chloride  placed  in  a  glass  funnel  over  a 
beaker,  should  be  used.  The  moisture  passing  through  the 
calcium  chloride  into  the  beaker.  Caustic  soda  should  be 
used  in  another  beaker  in  the  Balance  with  the  chloride. 

3 


30  THE  USE  AND  CARE  OF  A  BALANCE 

Fresh  calcium  chloride  should  be  added  from  time  to 
time. 

Eighth. — When  a  balance,  after  having  been  thoroughly 
cleaned,  is  found  to  have  lost  in  sensibility,  the  knife- 
edges  are  worn  and  dull  and  must  be  sharpened.  They 
should  be  attended  to  at  once  by  a  manufacturer  or  a 
balance  expert. 

VIBRATION. 

The  best  results  are  not  obtained  from  a  balance  that 
is  subject  to  vibration.  Nearly  every  laboratory  is  sub- 
ject to  more  or  less  vibration,  but  in  the  laboratories  of 
large  concerns  this  is  a  particularly  trying  problem,  as 
they  are  often  improvised  in  a  portion  of,  or  near,  a 
building  or  buildings  containing  heavy  machinery,  or 
near  railroad  tracks,  etc.,  which,  when  operating  causes 
a  constant  vibration,  impairing  accurate  weighing.  This 
has  been  made  a  subject  of  experiment,  and  a  number  of 
fairly  satisfactory  methods  have  been  devised  for  over- 
coming vibration. 

At  the  United  States  Metal  Company,  Grasselli,  Ind., 
holes  are  drilled  in  a  table  top  about  one-third  the  depth 
of  a  No.  5  rubber  stopper.  Number  five  stoppers  are 
inserted  into  the  holes  and  a  piece  of  lead  weighing  about 
J5O  pounds  measuring  a  little  longer  and  wider  than  a 
balance  case  is  placed  upon  the  stopper.  A  heavy  stone 
slab  or  a  cast  iron  block  would  answer  just  as  well.  The 


THE  USE  AND  CARE  OF  A  BALANCE  31 

idea,  however,  is  to  get  as  much  weight  as  possible.  The 
balance  is  placed  upon  this  slab. 

At  the  laboratory  of  the  Bethlehem  Steel  plant,  pillars 
of  iron  are  embedded  in  a  bed  of  sand  in  the  basement  of 
the  building,  the  pillars  coming  up  through  the  floor.  A 
slab  is  placed  upon  these  pillars,  the  top  of  which  is 
about  the  height  of  an  ordinary  balance  table  from  the 
floor.  This  has  been  found  very  satisfactory  where 
heavy  trains  are  constantly  passing  the  laboratory. 

Where  the  installation  of  the  above  mentioned  methods 
are  not  practical  for  various  reasons,  I  would  advise  the 
following  for  ordinary  purposes.  Cut  down  two  No.  5 
stoppers  about  one-third  from  the  top.  They  must  have 
one  hole  through  the  center.  Place  these  under  the 
front  set  screws  of  the  balance,  with  the  plug  of  the  set 
screw  resting  in  the  hole  of  the  stopper.  For  the  rear 
post  of  the  balance  use  a  whole  stopper.  This  method 
proves  very  satisfactory  for  ordinary  purposes. 

THE  STAUDINGER  BALANCE. 

The  Staudinger  balance,  sold  by  Arthur  H.  Thomas 
Co.,  is  so  different  in  construction  from  the  other  stand- 
ard balances  in  general  use,  that  it  requires  special 
adjusting  instructions. 

The  bearings  for  stirrups  and  beams  are  of  agate.  The 
front  pillars,  a,  a,  a,  have  a  groove  for  the  screw  point  to 


32  THE  USE  AND  CARE  OF  A  BALANCE 

rest  into ;  while  the  rear  pillars  have  a  cone  shaped  socket 
for  the  screw  point  to  rest  into.  The  pillar,  a,  a,  a,  must  be 
set  so  that  the  groove  is  in  a  direct  line  with  the  knife- 
edges  ;  thus,  looking  from  the  top,  o and  not,  thus, 

The  beam  should  be  supported  by  the  two  screws  in 
the  center  knife  edge  and  the  two  screws  f,  f  Fig.  17 
and  1 8. 


Fig.   17. — Stirrups  and  stirrup  support.     Staudinger  balance. 

When  upon  releasing  the  beam  on  these  balances,  the 
index  deviates  towards  or  from  the  index  plate,  it  is 
adjusted  by  the  screws  in  the  center  knife-edges.  That 
is,  if  the  index  deviates  towards  the  index  plate,  the 


THE  USE  AND  CARE  OF  A  BALANCE  33 

screw  in  the  front  of  the  center  knife-edge  must  be 
screwed  downward,  until  the  index  remains  stationary 
upon  releasing  the  beam;  if  it  deviates  from  the  index 
plate,  the  screw  in  the  back  of  the  center  knife-edge  must 
be  screwed  downward.  Judgment  must  be  used  in 
either  case.  If  the  center  knife-edge  raises  sufficiently 
from  the  plane,  to  allow  the  opposite  screw  to  be  raised, 
this  should  be  done.  That  is,  if,  as  in  the  first  case,  the 


Fig.    1 8. — End   knife   edge.   Staudinger   balance. 

index  goes  towards  the  index  plate,  and  the  knife-edge  is 
sufficiently  raised  from  the  plane,  to  allow  the  rear  screw 
to  be  raised,  it  should  be  done  instead  of  screwing  the 
front  one  downward.  Also,  in  the  other  case,  when  the 
index  moves  from  the  plate,  raise  the  front  screw  instead 
of  screwing  down  the  rear  one. 

When,  upon  releasing  the  beam  on  these  balances  the 
index  goes  to  the  right  or  left  and  back  again  to  the  zero 
point,  the  trouble  is  with  the  stirrups.  One  of  them  is 


34  THE  USE  AND  CARE  OF  A  BALANCE 

lifting  up  more  from  the  end  knife-edge  than  the  other, 
and  it  is  adjusted  by  the  screws  in  the  stirrups  c,  d  Fig. 
17.  The  one  that  raises  most  should  be  lowered  until  it 
raises  no  more  from  the  knife-edge  than  the  other.  Care 
must  be  taken  to  keep  the  stirrup  plane  parallel  with  the 
knife-edge. 

The  pillars  should  not  be  used  to  adjust  the  stirrups. 
If  the  beam  does  not  raise  from  the  center  bearing  re- 
move the  pillar.  A  screw  will  be  found  at  the  bottom 
of  a  rod  running  through  the  pillar.  Unscrew  this  screw 
until  the  beam  raises  so  that  daylight  can  be  seen  between 
the  center  knife-edge  and  the  plane.  The  two  screws,  f,  f 
Fig.  17  and  18,  in  beam  support  should  lightly  touch  the 
beam  when  beam  is  arrested. 

The  adjusting  weight  for  sensibility  on  this  balance  is 
on  the  back  of  the  center  knife-edge  and  is  raised,  to  raise 
the  sensibility  and  lowered  to  reduce  the  sensibility,  but 
always  to  correspond  with  a  certain  number  of  divisions 
upon  the  index  plate,  to  be  determined  by  placing  the 
rider  on  the  I  milligram  division  of  the  beam. 

ASSAY  BALANCES. 

Because  assay  balances  are  used  for  making  the  finest 
weighings,  their  construction  is  of  the  most  delicate 
order.  In  most  cases  their  adjustments  are  similar  to 
the  adjustments  on  an  analytical  balance.  Great  care 


THE  USE  AND  CARE  OF  A  BALANCE  35 

must  be  exercised  in  the  adjustment  of  an  analytical 
balance,  but  even  greater  care  should  be  taken  in  the  ad- 
justment of  an  assay  balance,  particularly  in  taking  the 
latter  apart  for  cleaning  and  dusting. 

The  arm  length  of  an  assay  balance  is  more  important 
than  the  arm  length  of  an  analytical  balance,  but  that  is 
not  discounting  the  importance  of  that  feature  of  the 
latter  balance.  This  is  because  there  are  more  direct 
weighings,  of  smaller  amounts,  on  the  assay  balance. 

The  arm  length  of  an  assay  balance  is  tested  in  the 
same  manner  as  that  of  an  analytical  balance,  save  only 
that  not  more  than  one  grm.  is  used  on  each  pan  of  the 
assay  balance. 

In  the  case  of  later  assay  balances,  sensible  to  1/200 
of  a  milligram  or  less,  more  than  one  gram  should 
never  be  placed  in  each  pan.  On  some  of  the  older 
styled  assay  balances,  however,  as  much  as  five  grams, 
may  be  safely  placed  in  each  pan. 

On  account  of  the  extreme  delicacy  of  these  balances, 
only  the  arm  length  and  sensibility  tests  should  be  made, 
and  no  other  adjustments  should  be  attempted  by  the 
user. 

TO  REPLACE  THE  GLASS  BASE. 

In  case  the  glass  base,  with  which  some  balances  are 
equipped  becomes  broken,  and  it  would  be  inconvenient 
to  send  the  balance  to  the  factory  to  have  the  broken  base 


36  THE  USE  AND  CARE  OF  A  BALANCE 

replaced,  the  user  may  replace  it  himself  by  exercising 
particular  care  in  following  the  rule  outlined  below.  In 
ordering  the  new  plate  be  sure  to  give  the  exact  thickness 
of  the  broken  plate,  and  the  name  and  the  number  of  the 
balance,  and  the  date,  as  nearly  as  possible,  when  the 
balance  was  purchased  from  the  manufacturer. 

To  put  on  a  new  plate,  first  remove  beam,  bows  and 
pans,  and  stirrups;  remove  pillar  and  rider  apparatus; 
take  out  draw  and  front  and  rear  frames;  draw  up  the 
sash  cords  and  tie  them  together,  so  as  to  keep  the 
weights  in  their  proper  position  in  the  frame  pillar;  lay 
the  case  flat,  and  remove  the  four  nuts  at  the  bottom  of 
the  case;  then  replace  the  Balance  in  its  natural  position 
and  then  lift  off  the  top  part  of  the  case.  There 
are  four  washers,  or  there  should  be,  on  the  top  of  the 
cloth  where  the  rods  that  hold  the  case  together  run 
through.  Be  sure  to  replace  these  washers.  Remove  all 
traces  of  broken  glass,  dust,  etc.,  from  the  cloth. 

Then  screw  on  the  pan  arrest  supports  to  the  glass 
base,  placing  that  support  with  the  longest  bearing  on  the 
screw  for  pan  arrest,  on  the  right  hand  side.  The  screws 
in  the  pan  arrest  supports  should  be  in  a  straight  line. 
See  that  the  bottom  of  the  glass  plate  is  perfectly  clean, 
and  the  cloth  washers  in  place  where  the  rods  run 
through.  Place  the  plate  upon  the  balance  base  and  put 


THE  USE  AND  CARE  OF  A  BALANCE  37 

top  of  case  in  position ;  put  the  rods  through,  and  screw 
tightly  with  the  nuts  at  the  bottom  of  the  case,  not  adding 
too  much  pressure,  but  sufficient  to  hold  the  case  in  place. 
Replace  the  pillar,  rider  apparatus,  beam,  stirrups  and 
bows  and  pans.  Replace  the  rear  frame. 

In  putting  on  a  new  plate  it  often  happens  that  the  pan 
arrest  plunger  appears  too  long  or  too  short.  This  may, 
at  times,  be  regulated  by  moving  the  plate  backwards  or 
forwards,  as  the  case  may  necessitate. 

If  care  is  taken  to  give  the  exact  thickness  of  the  plate 
and  the  balance  number,  when  ordering  the  plate  from 
the  balance  manufacturer  or  agent,  there  should  be  no 
trouble  experienced  in  putting  it  on. 


38  THE  USE  AND  CARE  OF  A  BALANCE 

WEIGHTS. 


KINDS  OF  WEIGHTS. 

The  writer  has  had  fourteen  years  experience  in  the 
making  and  adjusting  of  analytical  and  assay  weights 
with  one  of  the  foremost  manufacturers  in  this  country, 
besides  ten  years  experience  on  the  road  visiting  the 
laboratories  of  universities  and  colleges  and  commercial 
laboratories.  His  range  of  observation  has  been  large 
and  complete,  and  his  opportunity  for  the  careful 
study  of  this  more  than  sadly  neglected  com- 
mercial necessity  has  been  equally  so.  The  solu- 
tion of  the  weight  problem  has  not  been  improved 
upon  in  fifty  years.  However,  it  is  not  in  order  to 
discuss  the  problem  here,  and  the  writer  will  merely  en- 
deavor to  outline  the  best  way  of  utilizing  what  we  have. 

He  has  found  that  the  first  quality  lacquered  brass 
weights,  with  the  same  use  and  care,  retain  their  con- 
stancy longer  than  the  gold  or  so-called  platinum  plated 
weights.  Besides  the  gold  or  platinum  plating  on  the 
weights  appearing  not  up  to  the  standard  required  for 
this  kind  of  work,  he  has  found  also,  other  causes  for 
concluding  that  the  brass  lacquered  weight  is  the  best. 
Such  as  the  use  of  lead  shot  in  the  adjusting  of  so-called 
first  quality  weights.  The  lead  too  readily  oxidizes,  thus 
changing  the  original  weight.  For  these  reasons  he  would 


THE  USE  AND  CARE  OF  A  BALANCE  39 

recommend  the  brass  lacquered  ones   for  first  quality 
weights  for  analytical  purposes. 

CARE  OF  WEIGHTS. 

Ivory  pointed  or  tipped  forceps,  only,  should  be  used 
in  handling  analytical  weights.  They  should  never  be 
handled  with  the  fingers;  and  should  be  kept  as  free  as 
possible  from  all  acids  and  chemicals,  likely  to  corrode 
them. 

The  fractional  weights  should  be  wiped  as  frequently 
as  the  conditions  surrounding  them  require.  The  20  and 
the  two  10  milligram  weights,  which  are  often  made 
of  aluminum,  usually  get  a  trifle  heavier  after  they  have 
been  in  use  for  sometime,  and  require  a  little  more  care 
than  do  the  platinum  weights,  because  they  are  more 
readily  affected  by  acids  and  chemicals. 

STANDARD  FOR  CALIBRATING  WEIGHTS. 

Without  a  standard  weight,  the  exact  weight  of  the 
different  denominations  of  a  set  of  weights  cannot  be 
correctly  determined.  They  may  be  compared  with  each 
other,  but  no  positive  weights  can  be  deduced  by  calibrat- 
ing without  a  standard. 

I  would  suggest  that  every  laboratory  have  at  least  two 
standard  weights,  verified  by  the  Bureau  of  Standards  at 
Washington,  D.  C.  This  costs  very  little,  and  allows  of 
the  proper  determination  of  the  exact  weight  of  those  that 
are  put  to  general  use.  The  weights  most  convenient, 


4O  THE  USE  AND  CARE  OF  A  BALANCE 

or  rather,  most  desirable,  to  have  standardized  or  verified 
are  the  100  gram  and  the  I  gram. 

Having  these  two  weights  verified,  calibration  from  the 
100  gram  weight  down  through  the  set,  or  from  the  i 
gram  weight  up  may  readily  be  done ;  and  the  latter  may 
be  used  in  calibrating  the  fractional  weights.  The  posses- 
sion of  a  one  gram  standard  is  an  advantage  in  more  ways 
than  one.  Besides  allowing  calibrating  to  both  extremes, 
it  is  a  check  upon  the  100  gram  standard,  and  vice 
versa.  The  latter  will  be  used  less  however,  and  will  of 
course,  maintain  its  constancy  longer  than  the  one  gram. 
Where  the  standards  are  used  quite  often,  they  should 
be  verified  at  Washington  at  least  once  a  year;  but  if 
used  only  occasionally,  once  in  two  or  three  years  is 
sufficient,  where  the  weight  receives  especial  care. 

The  standardized  weights  should  never  be  used  in 
ordinary  weighing  but  only  used  while  calibrating.  They 
should  be  carefully  kept  in  a  covered  box. 

CALIBRATING  WEIGHTS. 

Place  the  larger  standard  weight  in  the  left  hand  pan 
of  the  balance,  and  all  the  weights  of  the  set 
from  and  including  the  50  grams  to  and  includ- 
ing the  i  gram  weights,  in  the  right  hand  pan,  to 
determine  the  error,  if  any,  between  the  standard  and 
the  fractional  weights.  Note  the  error,  if  any.  Then 


THE  USE:  AND  CARE  OF  A  BALANCE  41 

remove  the  standard,  placing  the  50  gram  weight  on  the 
left  hand  side,  leaving  the  remaining  fractional  weights 
on  the  right  hand  side.  Note  the  error,  if  any.  Then 
remove  the  50  gram  weight,  placing  the  20  gram 
weight  in  the  left  hand  pan,  and  the  two  10  only  in  the 
right  hand  pan,  removing  the  other  smaller  weights. 
Test  them  and  make  note  of  the  error,  if  any ;  and  pro- 
ceed by  removing  one  10  gram  weight,  and  placing  the 
5-2-2-1  gram  weights  on  the  right  hand  pan  with  the 
remaining  10  gram  weight,  and  note  error,  if  any.  Then 
remove  the  20  gram  weight,  and  all  the  weights  on 
the  right  hand  pan,  and  place  one  10  gram  weight  on  the 
left  hand  side  and  the  other  on  the  right  hand  side,  and 
test  the  two  for  error.  Note,  if  any.  Then  place  the 
five  grms.  weight  upon  the  left  hand  side  and  compare  it 
with  the  two  2  grams  and  the  one  gram  on  the  right  hand 
side,  and  note  error.  Compare  the  standard  one  gram 
weight  with  the  other,  placing  the  standard  on  the  left 
hand  pan,  and  note  error,  if  any. 

To  calibrate  the  fractional,  or  milligram,  weights, 
place  the  standard  one  gram,  weight  on  the  left  hand  side, 
and  the  fractional  weights  on  the  right  hand  side,  test 
and  note  error,  if  any.  Proceed  in  the  same  manner 
with  the  milligram  weights,  down  to  the  one  milligram 
weight,  as  in  the  calibration  of  the  gram  weights. 


42  THE  USE  AND  CARE  OF  A  BALANCE 

In  this  way  compare  the  errors  found  to  exist  with  the 
verified  standard  one  gram  weight,  and  the  verified 
standard  weight  of  100  grams  and  thereby  determine  the 
exact  error  in  each  individual  weight,  and  keep  copies  of 
the  result  of  the  calibration  for  use  in  weighing. 

RECIPE  FOR  LACQUER  FOR  ALUMINUM,  GERMAN 
SILVER  AND  BRASS. 

Into  four  ounces  of  pure  grain  alcohol  put  15  grams 
of  white  shellac.  Cork  well  and  allow  to  stand  several 
days.  Then  carefully  pour  off  the  clear  solution  from 
the  top  into  a  bottle.  If  necessary  put  through  a  filter 
paper.  This  makes  the  best  shellac  lacquer  for  German 
Silver  or  aluminum. 

The  same  proportion  of  orange  shellac  and  alcohol 
makes  a  lacquer  for  brass.  This  lacquer  may  be  used 
cold  or  the  metal  may  be  heated  slightly.  Care  must  be 
taken,  when  heating,  not  to  get  the  metal  too  hot,  as  the 
shellac  is  likely  to  blister. 


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HAI.L.IGAN  -  Fertility  and  Fertilizer  Hints.     8vo.     Pages  VIII  .4    156. 

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Eraser 
Use   of  a 


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QC107 
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311924 


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